Comprehensive Prevention and Control Techniques of Sweet Potato Stem Nematodiasis
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Sweet potato stem nematode disease is a serious and highly contagious issue in sweet potato cultivation. It spreads quickly and can affect the crop at multiple stages, including seedling, field growth, and storage. However, it primarily targets the tubers, causing damage that may not be immediately visible on the surface. The skin of infected sweet potatoes often appears brown, green, or cracked, and the internal tissue becomes soft and discolored. In some cases, the potatoes look normal externally, but the damage is hidden inside, which reduces both quality and yield significantly.
The disease is caused by a parasitic nematode, a small, slender worm with a pointed end, measuring between 0.9 to 1.45 mm in length. These nematodes can survive the winter as adults, larvae, or eggs within the tubers, and also remain in the soil and manure. They are sensitive to high temperatures, and soaking them in 50°C water for 10 minutes can kill up to 98% of them. However, they are resilient in cold conditions, surviving at -15°C without dying, and can endure dry environments for up to a year. This makes them difficult to eliminate once established.
To effectively manage this disease, several integrated strategies can be applied:
1. **Use of Resistant Varieties**: Selecting local varieties that are resistant to nematodes is crucial. Examples include Jinshu No. 10, Yushu No. 13, Sushu No. 8, and Beijing 553, which are well-suited for the Central Plains region and show good resistance.
2. **Cultivation of Disease-Free Seedlings**: Apply 60 grams of 3% carbofuran microgranules per square meter in the seedbed before covering the soil. Soak seed potatoes in 52–53°C warm water for 10 minutes before planting to kill nematodes. When transplanting, use aldicarb or methyl isothiazole solution to treat the base of the seedlings. High-cutting techniques can also help, where the roots are cut 3–5 cm above the ground and soaked in insecticides like phoxim or methyl isothiazole for 30 minutes.
3. **Establishment of Disease-Free Fields**: Use only healthy plots for planting, and ensure that seed potatoes and seedlings are free from infection. Summer crops should be planted using nursery-grown or spring-planted seedlings, and these should be grown in disease-free areas the following year.
4. **Chemical Control**: In heavily affected areas, apply 2000–2500 times diluted methyl isofluosal or phoxim. Pour 0.5 kg per hole when planting. Alternatively, use granular formulations such as olivine or stemline granules, applying 1–1.5 kg per hole and watering afterward. For mild infestations, soak the base of the seedlings in 150–200 times diluted insecticide for 30 minutes before planting.
5. **Elimination of Infected Materials**: Remove and destroy all diseased potatoes, plant residues, and contaminated soil. Do not use infected peels, washing water, or soil as fertilizer. Ensure all compost is fully fermented at temperatures above 50°C.
6. **Crop Rotation**: Avoid planting sweet potatoes in the same area for more than three years. Rotate with crops such as wheat, corn, millet, cotton, or tobacco to break the nematode life cycle.
7. **Adjust Planting and Harvesting Times**: In severe cases, delay planting until mid-May and harvest early, before the nematode population peaks. This helps reduce the risk of infection and ensures timely processing for food or feed.
8. **Strengthen Quarantine Measures**: Enforce strict regulations to prevent the movement of infected potatoes and seedlings across regions. This is essential to avoid spreading the disease further.
By combining these methods, farmers can significantly reduce the impact of sweet potato stem nematode disease and protect their crops effectively.